Strains produce a modification of the vibration properties of materials, which can be observed by Raman scattering: a compressive stress results in an increase of the Raman frequency shift, while tensile stress results in a decrease. On this line of arguments, in this work, we investigate adsorption strains in porous silicon by Raman spectroscopy.The adsorption of chemical species induces a compressive strain in the porous silicon due to the action of the molecular forces, as a consequences a reversible blue-shift of the Raman spectra of the sample has been observed.